Hi,
Welcome to the HCM
Brief...History is incomplete,some associated symptoms need to be known to differentiate differential diagnosis.
Detailed answer...
As I have gone through your question,I need to know about other associated symptoms to rule out wether it can be
chicken pox,
measles ,
eczema or low immunity.
If she has 2 to 3 days back history of runny nose,flu,red eyes or fever then most probably it can be viral infection (measles),as the spots tend to be in clusters and crust gradualy in chicken pox and they appear first on abdomen, in measles spots and rashes start appearing first on face but associated with above mentioned symptoms.
Since you have also mentioned about low immunity,with compromised immunity ,the child should have history of recurrent different infections or chest infections.
From my point of view it seems that she is having eczema only ,which is
allergic response of skin to cold weather,pollen etc .For that stop using soaps and apply amolients 3 times a day.She may also use
diphenhydramine ointment 2 times a day and follow accordingly.
Regards,Dr.Maheshwari